Support member for mounting a microelectronic circuit package

ABSTRACT

A Tape-Automated-Bonding (TAB) package includes a resilient polyimide layer that supports a metal leadframe. A microelectronic circuit die is mounted in a hole in the polyimide layer and interconnected with inner leads of the leadframe. The TAB package is adhered to a support member having spacers that abut against the surface of a printed circuit board (PCB) on which the package is to be mounted and provide a predetermined spacing between the leadframe and the surface. Outer leads that protrude from the leadframe are bent into a shape so as extend, in their free state, toward the surface at least as far as the spacers. The package and support member assembly is placed on the PCB surface, and the combination of the weight of the assembly, the resilience of the leads and the preset standoff height enable the leads to resiliently deform so that the spacers abut against the surface and the leads conformably engage with the surface for soldering or other ohmic connection to conjugate bonding pads on the surface. The support member can be formed with lead retainers around which the leads extend to form loops that resiliently and conformably engage with the surface as the assembly is lowered thereon. The support member maintains coplanarity, adds weight to the package, pre-sets the standoff to protect the formed outer leads during surface mounting and enables the package to be shipped without a separate carrier.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional of application Ser. No. 08/323,817 filed on Oct.17, 1994 now U.S. Pat. No. 5,673,479.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to the art of microelectroniccircuit fabrication, and more specifically to a microelectronic circuitleadframe package such as a Tape-Automated-Bonding (TAB) packageincluding integral support members for outer lead form protection duringmounting on a printed circuit board.

2. Description of the Related Art

Tape-Automated-Bonding (TAB), also known as Chip-on-Tape (COT), is asystem for assembling, shipping and mounting microelectronic circuitchips or dies that are integrally attached and interconnected to aflexible leadframe. TAB enables a large number of chip/leadframe modulesto be automatically fabricated with high speed and precision in aneconomical manner.

The TAB system fabricates a large number of identical leadframemetallization patterns on a roll of polyimide tape that is movablebetween reels through the required processing stations. The individualpatterns are cut from the roll to form leadframe packages.Microelectronic integrated circuit dies are mounted on the packages andinterconnected with the leadframes, and the resulting TAB/COT modulesare inserted into individual plastic carriers for shipping to end users.

A typical COT 10 is illustrated in FIG. 1, and comprises a flexiblepolyimide sheet or film 12 that is formed with peripheral perforations14 to enable reel-to-reel transport of the roll from which the film 12was cut using a sprocket (not shown). The film 12 is formed with acentral hole 16 for receiving a microelectronic circuit die or chip 18.

The COT 10 further comprises a leadframe 20 that is formed on the film12 as a metallization pattern. The leadframe 20 includes a plurality ofleads 22 that extend laterally outward from bonding pads or terminals 24(see FIG. 3) on the chip 18 to test pads 26 that are located adjacent tothe periphery of the film 12. Each lead 22 includes an inner portion 22athat extends from the chip 18 to the edge of the hole 16, anintermediate portion 22b that extends under an optional protective epoxylayer 28, an outer portion 22c and a peripheral portion 22d thatinterconnects with the respective test pad 26.

The film 12 is further formed with excise apertures or holes 30 throughwhich the outer portions 22c of the leads 22 extend. After the COT 10has been received by the end user, it is tested using the test pads 26.The COT 10 is then subjected to further processing including excisingthe inner portion of the leadframe 20 and the chip 18 from the film 12.This is performed by severing the outer portions 22c of the leads 22 atthe outer edges of the holes 30, and cutting webs 32 that connect theportion of the film 12 laterally inward of the holes 30 from theremainder of the film 12.

A module 34 that results from the excise step is illustrated in FIG. 2,and consists of the leadframe 20 with the peripheral portions 22d of theleads 22 removed, and the chip 18. The outer portions 22c of the leads22 are redesignated as 36.

Although only a few leads are shown in FIGS. 1 and 2 for clarity ofillustration, the leadframe 20 of an actual COT 10 includes a muchlarger number of leads, typically hundreds, that are spaced from eachother by a pitch of less than 100 micrometers. The outer leads 36 asviewed in FIG. 2 are extremely thin and fragile, and can be easilydeformed and/or damaged.

For this reason, the COT 10 cannot be handled or shipped in theconfiguration illustrated in FIG. 2 with the leads 36 free. It isnecessary to the maintain the COT 10 in the form illustrated in FIG. 1until it is to be mounted on a printed circuit board (PCB) or othersurface, including providing a protective carrier in which the COT 10 isretained for shipping. The carrier is necessarily larger and weighs morethan the COT 10. This introduces increased shipping charges, in additionto the cost of the carrier itself.

Some leadframe packages have leads that are sufficiently large andstrong that they can be bent into a conventional "gull-wing" or othersuitable shape and provide sufficient rigidity for unsupported mountingon a PCB. The thin leads of the COT 10, however, are not able to supportthe weight of the assembly 34, and will collapse if an attempt is madeto surface mount the module 34 of FIG. 2 in this manner.

For this reason, the COT 10 is conventionally mounted on a PCB 38 orother supporting surface formed with conjugate bonding pads or terminals40 using a "hot bar" process as illustrated in FIG. 3. The COT 10 ismoved to an excise station, while remaining in its protective carrier,where the leadframe 20 and chip 18 are removed from the outer portion ofthe film 12 and picked up by a vacuum arm. During this excise operation,the leads 36 are bent into a gull-wing shape as illustrated in thedrawing.

The module 34, as excised from the COT 10 and having the leads formedinto the gull-wing shape, is then placed by the arm 42 onto the PCB 38with the leads 36 in contact with the terminals 40. A hot bar 44 pressesthe leads 36 against the terminals 40 and causes solder that waspreviously coated on the terminals 40 to reflow and ohmically adhere theleads 36 to the terminals 40.

Although capable of providing the required function of TAB mounting, thehot bar apparatus is expensive and slow, and is therefore impracticalfor small scale users to acquire. In addition, the conventional systemfor packaging, shipping and mounting COTs suffers from other drawbacksand disadvantages.

Due to the fragility of the outer leads, reworking of mounted COTs tocorrect, for example, defective solder joints is impractical. Removal ofdefective COTs after mounting is also difficult, since the fragile leadsare easily broken and can remain attached to the PCB. It is alsoexcessively difficult to test a COT after it has been excised from thepackage as illustrated in FIG. 1 and assumes the form illustrated inFIG. 2 due to the small size, extreme flexibility and fragility of theleads 36.

SUMMARY OF THE INVENTION

The present invention provides an improved Tape-Automated-Bonding (TAB)or Chip-on-Tape (COT) microelectronic circuit leadframe packagestructure including integral support members for outer lead protectionand mounting, and a method for mounting the package on a printed circuitboard or other surface.

In accordance with the present invention, a TAB package includes aresilient polyimide layer that supports a metal leadframe. Amicroelectronic circuit die is mounted in a hole in the polyimide layerand interconnected with inner leads of the leadframe.

The TAB package is adhered to a support member having spacers that abutagainst the surface of a printed circuit board (PCB) on which thepackage is to be mounted and provide a predetermined spacing between theleadframe and the surface.

Outer leads that protrude from the leadframe are bent into a shape so asextend, in their free state, toward the surface at least as far as thespacers. The package and support member (spacer) assembly is placed onthe PCB surface, and the weight of the assembly in combination with theresilience of the leads and their formed shape enables the leads toresiliently deform so that the spacers abut against the surface and theleads conformably engage with the surface for soldering or other ohmicconnection to conjugate bonding pads on the surface.

The support member can be formed with lead retainers around which theleads extend to form loops that resiliently and conformably engage withthe surface as the assembly is lowered thereon.

The support member protects the outer leads, and enables the presentstructure to be shipped without a separate carrier. The increasedintegrity that is imparted to the outer leads by the support memberenables the structure to be electronically tested after it has beenreceived by an end user. Reworking after mounting is also possible dueto the increased lead integrity.

The present structure can also be surface mounted without the use of ahot bar apparatus. This provides TAB/COT capability to small scale usersthat do not have sufficient resources to acquire a hot bar apparatus. Italso allows TAB/COT to be surface mounted in the same manner as otherperipherally leaded devices.

These and other features and advantages of the present invention will beapparent to those skilled in the art from the following detaileddescription, taken together with the accompanying drawings, in whichlike reference numerals refer to like parts.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view illustrating a conventional Tape-Automated-Bonding(TAB) or Chip-on-Tape (COT) microelectronic circuit package with anintegrated circuit die or chip mounted thereon;

FIG. 2 is a plan view illustrating a lead frame assembly of the TABillustrated in FIG. 1, with the microelectronic circuit chip mountedthereon, after excise from the TAB;

FIG. 3 is a sectional view illustrating a conventional "hot bar" processfor mounting a TAB package on a printed circuit board;

FIG. 4 is a sectional view illustrating a microelectronic circuitpackage according to the present invention prior to mounting on aprinted circuit board or other surface;

FIG. 5 is similar to FIG. 4, but illustrates the present structure aftermounting on the printed circuit board;

FIG. 6 is a sectional view illustrating another microelectronic circuitpackage according to a variation on the present invention prior tomounting on a printed circuit board or other surface;

FIG. 7 is similar to FIG. 6, but illustrates the structure aftermounting on the printed circuit board;

FIG. 8 is a plan view illustrating a support member of themicroelectronic circuit structure illustrated in FIGS. 6 and 7;

FIG. 9 is a plan view illustrating a lead frame package assembly,including outer leads that are retained by optional lead bars;

FIGS. 10 and 11 are sectional views illustrating a method of assemblingthe microelectronic circuit assembly of FIGS. 6 and 7; and

FIGS. 12 to 17 are sectional views illustrating alternative embodimentsof the present microelectronic circuit structure.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of a microelectronic integrated circuit structure50 according to the present invention is illustrated in FIGS. 4 and 5.The structure 50 comprises a Tape-Automated-Bonding (TAB) orChip-on-Tape (COT) lead frame 52, which comprises a flexible polyimidesheet or film 54. A metallization pattern comprising a plurality ofelectrically conductive leads 56 is formed on the film 54.

The lead frame 52 per se is essentially similar to the leadframe 20illustrated in FIG. 1. The film 54 is formed with a central hole 58.Inner ends of the leads 56 extend over the hole 58, and are soldered orotherwise ohmically adhered to conjugate terminals on a microelectronicintegrated circuit die or chip 60. In this manner, the chip 60 issupported by the lead frame 52 and electrically interconnectedtherewith. The leads 56 extend laterally outward from the film 54 toconstitute outer leads that are redesignated as 62.

The structure 50 comprises a heatspreader 84 including a body 86 onwhich the leadframe 52 is adhered by means such as an adhesive 68, withthe leadframe 52 being disposed between the support member 84 and asurface 69 of a printed circuit board (PCB) or other member on which thestructure 50 is to be mounted as illustrated in FIG. 5. The heatspreader84 is preferably stamped from a thermally conductive material that hasthe required physical properties and weight, and is formed with a cavity88.

The chip 60 is adhered to the upper wall of the cavity 88 by a thermallyconductive adhesive 90. Spacers 92 extend from the body 86 toward thesurface 69 through holes 94 formed through the leadframe 52 in areaswhere the leads 62 are not present.

The ends of the leads 62 are bent into a gull-wing or other suitableshape with a positive toe angle such that the ends of the leads 62 arespaced from the leadframe 52 by a distance D2 in their free state asillustrated in FIG. 4. The distance D2 is equal to or larger than adistance Dl between the leadframe 52 and the ends of the spacers 92.

When the structure 50 is placed on the surface 69 for mounting, theleads 62 resiliently deform in such a manner as to conformably engagewith bonding pads or terminals 80 on the surface 69 as illustrated inFIG. 5. The structure 50 is permanently attached to the surface 69 byapplying heat such that solder (not shown) which was previously coatedon the terminals 80 reflows and ohmically adheres the leads 62 to theterminals 80.

The weight of the heatspreader 84 is selected such that, in response tothe total weight of the structure 50 and the resilience of the leads 62and their formed shape, the leads 62 resiliently deform as the structure50 is lowered onto the surface 69, and the ends of the spacers 92 abutagainst the surface 69.

This enables the structure 50 to be mounted without the use of a hot baras is required in the prior art, since the spacers 92 render thestructure 50 self-supporting. The spacers 92 provide the optimal spacingbetween the leadframe 52 and the surface 69, while the leads 62 areallowed to resiliently conform to the surface 69.

If desired, optional lead bars 78 of an electrically insulative materialsuch as polyimide can be attached to the leads 62 as illustrated. Thelead bars 78 can also be advantageously be provided outside (beyond) thelead tips, although not explicitly shown. The illustrated arrangementincluding the heatspreader 84 is especially advantageous in that theheatspreader 84 provides, in addition to its primary function of outerlead form protection during mounting, a secondary function ofdissipating heat generated during operation of the chip 60.

In the above description, it was assumed that the thickness of theterminals 80 was negligible. If the terminals 80 have significantthickness, the distance D2 between the ends of the leads 62 and theleadframe 52 can be reduced accordingly in order to provide the requiredresilience for the leads 62. It will be noted that the resilience of theleads 62 provides the additional advantage of compensating for relativethermal expansion of the leads 62 and the terminals 80 during solderreflow.

The structure 50 is also adaptable to a configuration in which the endsof the leads 62 are designed to be nominally coplanar with the ends ofthe spacers 92, such that D2 =D1. However, due to manufacturingtolerances, some of the leads 62 will protrude beyond the ends of thespacers 92 such that D2 >D1. In such a case, the leads 62 that extendbeyond the spacers 92 are capable of being resiliently deformed asdescribed above to maintain coplanarity of the leads 62 and the surface69.

In this variation, some of the leads 62 can also extend toward thesurface 69 by a distance that is less than that of the spacers 92, suchthat D2 <D1. In this case, the resulting gap is filled by the solderthat is used to ohmically adhere the leads 62 to the terminals 80.

An alternative microelectronic integrated circuit structure 51 embodyingthe present invention is illustrated in FIGS. 6 to 8, in which likeelements are designated by the same reference numerals used in FIGS. 4and 5. The structure 51 comprises a support member 64 including a base66 on which the leadframe 52 is adhered by means such as an adhesive 68.The base 64 is formed with a central hole 67.

The support member 64 is preferably injection molded from a thermallyconductive and electrically insulative material such as polyphenylsulfide (PFS), although the invention is not limited to any particularmaterial. The support member 64 can be formed of any suitable materialthat has the required physical properties and weight.

Whereas the leadframe 52 is disposed between the support member(heatspreader) 84 and the surface 69 in the structure 50, the supportmember 64 is disposed between the leadframe 52 and the surface in thestructure 51.

The support member 64 comprises one or more spacers 70 that extend awayfrom the base 66 and the leadframe 52 toward the surface 69. The spacers70 are illustrated as being embodied as elongated pins or rods, althoughthe scope of the invention is not so limited.

The structure 51 further comprises a lead retainer 72 in the form of aperipheral, outwardly slanting edge that extends from the base 54 towardthe surface 69. The retainer 72 has an end 74 that faces the surface 69.The spacers 70 have ends 76 that similarly face the surface 69. Thedistance from the ends 76 to the leadframe 52 are D1 as described abovewith reference to the structure 50 of FIGS. 4 and 5, whereas thedistance from the end 74 to the leadframe 52 is less than D1.

The outer leads 62 are bent inwardly around the laterally outer surfaceand the end 74 of the lead retainer 72. As further illustrated in FIG.9, lead bars 78 of an electrically insulative material such as polyimideare adhered to the end portions of the leads 62 and are themselvesadhered to the inner surface of the retainer 72. In this manner, theleads 62 form loops that extend around the end 74 of the retainer 72.

As illustrated in FIG. 6, the structure 51 is positioned above thesurface 69, and the ends of the loops of the leads 62 extend, in a freestate, from the leadframe 52 by the distance D2 that is equal to orgreater than the distance D1. As illustrated in FIG. 7, the structure 51is mounted on the surface 69 such that the ends 76 of the spacers 70abut against the surface 69.

The leads 62 are capable of resiliently deforming in such a manner as toconformably engage with the terminals 80 on the surface 69. Thestructure 51 is permanently attached to the surface 69 by soldering asdescribed above.

The weight of the support member 70 is selected such that, in responseto the total weight of the structure 51 and the resilience of the leads62 and their formed shape, the leads 62 are capable of resilientlydeforming as the structure 51 is lowered onto the surface 69, and theends 74 of the spacers 70 abut against the surface 69.

The support member 64 protects the outer leads 62, and enables thestructure 51 to be shipped without a carrier. The increased integritythat is imparted to the outer leads 62 by the support member 64 enablesthe structure 51 to be electronically tested after it has been receivedby an end user prior to mounting. Reworking after mounting is alsopossible due to the increased lead integrity.

FIGS. 10 and 11 illustrate a method of fabricating the structure 51. InFIG. 10, the leadframe 52 and chip 60 are excised from the outer portionof the COT module, and the lead bars 78 are adhered to the leads 62. InFIG. 11, the adhesive 68 is applied to the base 66 of the support member64 (and/or to the film 54 of the leadframe 52), and the leadframe 52 isadhered to the support member 64. The leads 62 are bent down and aroundthe end 74 of the lead retainer 72, and the lead bar 78 is adhered tothe lead retainer 72 to produce the structure 51 as illustrated in FIG.6.

In the structure 51 of FIG. 6, the leadframe 52 is mounted with the film54 facing the support member 64. FIG. 12 illustrates a structure 51'which is similar to the structure 51 except that the leadframe 52 ismounted with the film 54 facing away from the support member 64 and thechip 60 facing the surface 69. The invention is not so limited, however,and encompasses mounting the chip 60 on the upper, rather than the lowersurface of the leadframe 52.

FIG. 13 illustrates another structure 100 embodying the presentinvention in which the functions of the spacers 70 and lead retainer 72as illustrated in FIG. 6 are combined. The structure 100 comprises asupport member 102 having a base 104, and a spacer 106 that has a shapesimilar to that of the lead retainer 72. The leads 62 are looped aroundthe end of the spacer 106 and adhered to the laterally inner surfacethereof by the lead bars 78 in the manner described above with referenceto FIG. 6.

As the structure 100 settles onto the surface 69 due to its weight, theleads 62 resiliently bend into the shape illustrated in FIG. 14. At thispoint, the end of the support member 102 abuts against the surface 69with the leads 62 pressed therebetween. The leads 62 are then solderedto terminals (not shown) on the surface 69 as described above.

FIG. 15 illustrates another structure 110 embodying the presentinvention which combines the concepts of the heatspreader 84 of FIG. 4with the combined spacer/lead retainer 106 of FIG. 13. The structure 110comprises a heatspreader 112 including a base 114 and a spacer 116. Theleads 62 are looped over the inner surface and end of the spacer 116,and adhered to the outer surface of the spacer 116 via the lead bar 78.The operation of mounting the structure 110 is the same as describedwith reference to FIG. 14.

FIG. 16 illustrates a structure 120 comprising a heatspreader 122 inwhich the relative positions of the spacer and the lead retainer arereversed from the embodiments described above. More specifically, theheatspreader 122 comprises a base 124, a spacer 126 and a retainer 128that is spaced laterally inward of the spacer 126. The leads 62 looparound the outer surface and the end of the retainer 128 and are adheredto the inner surface thereof.

FIG. 17 illustrates a structure 120' that is similar to the structure120 except that the leads 62 are looped around the inner surface and theend of the retainer 128 and are adhered to the outer surface thereof.

Various modifications will become possible for those skilled in the artafter receiving the teachings of the present disclosure withoutdeparting from the scope thereof.

For example, the spacers and/or retainers can be provided in anysuitable number and have any suitable shape. It is even within the scopeof the invention to provide a support member comprising only one spacerin the form of a block, although not specifically illustrated.

I claim:
 1. A support member for mounting a microelectronic circuitpackage, including a microelectronic device and a leadframe having aplurality of leads protruding outwardly therefrom, on a surface,comprising:a base for supporting said package; a spacer that extendsfrom said base for abutment against said surface to provide apredetermined spacing between said leadframe and said surface; whereinsaid leads are configurable such that, in a free state, said leadsextend toward said surface at least as far as said spacer; and inresponse to a combined weight of said package and said support member,said leads are capable of resiliently deforming such that said spacerabuts against said surface and said leads conformably engage with saidsurface; and a lead retainer that extends from said base toward saidsurface; wherein said leads have end portions that are attachable tosaid lead retainer such that, in said free state, said leads form loopsthat extend toward said surface beyond said spacer; wherein said leadretainer has an end that faces said surface and said leads areextendable around said end; wherein said leadframe is disposed betweensaid support member and said surface, and said leads are extendable fromsaid leadframe around a laterally inner surface of said lead retainerand said end of said lead retainer, and said end portions are attachableto a laterally outer surface of said lead retainer.
 2. The supportmember of claim 1 wherein said lead retainer is disposed laterallyinward of said spacer.
 3. The support member of claim 1 wherein saidleadframe includes a film, and outer portions of said leads extendoutwardly beyond said film.
 4. A support member for mounting amicroelectronic circuit package, including a microelectronic device anda leadframe having a plurality of leads protruding outwardly therefrom,on a surface, comprising:a base for supporting said package; a spacerthat extends from said base for abutment against said surface to providea predetermined spacing between said leadframe and said surface; whereinsaid leads are configurable such that, in a free state, said leadsextend toward said surface at least as far as said spacer; and a leadretainer extending from said base toward said surface; said leads, inthe free state, forming loops that extend about said lead retainertoward said surface beyond said spacer; wherein said lead retainer hasan end that faces said surface, and said leads are extendable aroundsaid end; and wherein said leads are extendable from said leadframearound a laterally inner surface and said end of said lead retainer, andsaid leads have end portions attachable to a laterally outer surface ofsaid lead retainer.
 5. The support member of claim 4 wherein said leadretainer is disposed laterally inward of said spacer.
 6. The supportmember of claim 4 wherein said leadframe is disposed between saidsupport member and said surface.
 7. The support member of claim 4wherein said leadframe includes a film, and outer portions of said leadsextend outwardly beyond said film.
 8. A support member for mounting amicroelectronic circuit package, including a microelectronic device anda leadframe having a plurality of leads protruding outwardly therefrom,on a surface, comprising:a base for supporting said package; and aspacer that extends from said base for abutment against said surface toprovide a predetermined spacing between said leadframe and said surface;said leads are configurable such that, in a free state, said leadsextend toward said surface at least as far as said spacer, and inresponse to a combined weight of said package and said support member,said leads are capable of resiliently deforming such that said spacerabuts against said surface and said leads conformably engage with saidsurface; said spacer has its outboard surface projecting laterallyoutward relative to said base; said base and said spacer being formed asa single unit; and said leads wrap around said spacer.
 9. The supportmember of claim 8 wherein said leads wrap around an inboard surface ofsaid spacer, around a free end of said spacer and to said outboardsurface of said spacer.
 10. The support member of claim 8 wherein saidleadframe includes a film, and outer portions of said leads extendoutwardly beyond said film.
 11. The support member of claim 8 whereinsaid leadframe includes an opening in which said microelectronic deviceis positioned.
 12. A support member for mounting a microelectroniccircuit package, including a microelectronic device and a leadframehaving a plurality of leads protruding outwardly therefrom, on asurface, comprising:a base for supporting said package; and a spacerthat extends from said base for abutment against said surface to providea predetermined spacing between said leadframe and said surface; saidleads are configurable such that, in a free state, said leads extendtoward said surface at least as far as said spacer, and in response to acombined weight of said package and said support member, said leads arecapable of resiliently deforming such that said spacer abuts againstsaid surface and said leads conformably engage with said surface; saidbase has a base end, and said spacer extends outwardly from said baseend and angularly towards said surface; said leadframe includes a film,and outer portions of said leads extend outwardly beyond said film; saidouter portions loop around said spacer; and said spacer has an outboardsurface projecting laterally outward relative to said base.
 13. Thesupport member of claim 12 wherein said outer portions wrap around saidoutboard surface, around a free end of said spacer and to an inboardsurface of said spacer.
 14. The support member of claim 13 wherein saidbase is disposed between said leadframe and said surface.
 15. Thesupport member of claim 12 wherein said outer portions wrap around aninboard surface of said spacer, around a free end of said spacer and tosaid outboard surface of said spacer.
 16. The support member of claim 15wherein said leadframe is disposed between said base and said surface.17. The support member of claim 12 wherein said base has an opening, andsaid microelectronic device is disposed in said opening.
 18. The supportmember of claim 12 wherein said base includes a cavity, and saidmicroelectronic device is mounted in said cavity.
 19. The support memberof claim 12 wherein a lead bar is attached to said outer portions forattachment to said spacer.
 20. The support member of claim 12 whereinsaid outer portions are attached to said outboard surface of saidspacer.
 21. The support member of claim 12 wherein said base and saidspacer are formed as a single unitary unit.
 22. The support member ofclaim 12 wherein a lead bar is attached to said leads for attachment tosaid spacer.
 23. A support member for mounting a microelectronic circuitpackage, including a microelectronic device and a leadframe having aplurality of leads protruding outwardly therefrom, on a surface,comprising:a base for supporting said package; a spacer that extendsfrom said base for abutment against said surface to provide apredetermined spacing between said leadframe and said surface; saidleads are configurable such that, in a free state, said leads extendtoward said surface at least as far as said spacer; and in response to acombined weight of said package and said support member, said leads arecapable of resiliently deforming such that said spacer abuts againstsaid surface and said leads conformably engage with said surface; and alead retainer that extends from said base toward said surface; saidleadframe includes a film, and outer portions of said leads extendoutwardly beyond said film; said outer portions have end portions thatare attachable to said lead retainer such that, in said free state, saidouter portions form loops that extend toward said surface beyond saidspacer; and said lead retainer has an outboard surface projectinglaterally outward relative to said base.
 24. The support member of claim23 wherein said outer portions wrap around said outboard surface, arounda free end of said lead retainer and to an inboard surface of said leadretainer.
 25. The support member of claim 23 wherein said support memberis disposed between said leadframe and said surface, said outer portionsare extendable from said leadframe around a laterally outer surface ofsaid end of said lead retainer, and said end portions are attachable toa laterally inner surface of said lead retainer.
 26. The support memberof claim 23 wherein said leadframe is disposed between said supportmember and said surface, said outer portions extend around a laterallyinner surface of said end of said lead retainer, and said end portionsare attachable to a laterally outer surface of said lead retainer. 27.The support member of claim 23 wherein said base has an opening in whichsaid microelectronic device is positioned.
 28. The support member ofclaim 23 wherein a lead bar is attached to said outer portions forattachment to said lead retainer.
 29. A support member for mounting amicroelectronic circuit package, including a microelectronic device anda leadframe having a plurality of leads protruding outwardly therefrom,on a surface, comprising:a base for supporting said package; a spacerthat extends from said base for abutment against said surface to providea predetermined spacing between said leadframe and said surface; saidleads are configurable such that, in a free state, said leads extendtoward said surface at least as far as said spacer; and in response to acombined weight of said package and said support member, said leads arecapable of resiliently deforming such that said spacer abuts againstsaid surface and said leads conformably engage with said surface; and alead retainer that extends from said base toward said surface; saidleadframe includes a film, and outer portions of said leads extendoutwardly beyond said film; said outer portions have end portions thatare attachable to said lead retainer such that, in said free state, saidouter portions form loops that extend toward said surface beyond saidspacer; and said lead retainer is disposed laterally inward of saidspacer.
 30. The support member of claim 29 wherein said base includes anouter end, and said spacer extends perpendicularly from said base,spaced a distance inward from said outer end.
 31. A support member formounting a microelectronic circuit package, including a microelectronicdevice and a leadframe having a plurality of leads protruding outwardlytherefrom, on a surface, comprising:a base for supporting said package;a spacer that extends from said base for abutment against said surfaceto provide a predetermined spacing between said leadframe and saidsurface; and a lead retainer extending from said base toward saidsurface; wherein said leads, in the free state, form loops that extendabout said lead retainer toward said surface beyond said spacer; whereinsaid lead retainer has its outboard surface projecting laterally outwardrelative to said base.
 32. The support member of claim 31 wherein saidleads wrap around said outboard surface, around a free end of said leadretainer and to an inboard surface of said lead retainer.
 33. Thesupport member of claim 31 wherein said leadframe includes a film, andouter portions of said leads extend outwardly beyond said film.
 34. Thesupport member of claim 31 wherein said lead retainer extends outwardlyaway from said spacer.
 35. The support member of claim 31 wherein inresponse to a combined weight of said package and said support member,said leads are capable of resiliently deforming such that said spacerabuts against said surface and said leads conformably engage with saidsurface.
 36. The support member of claim 31 wherein said support memberis configured to be disposed between said leadframe and said surface.37. The support member of claim 31 wherein said lead retainer isdisposed laterally outward of said spacer.
 38. A support member formounting a microelectronic circuit package, including a microelectronicdevice and a leadframe having a plurality of leads protruding outwardlytherefrom, on a surface, comprising:a base for supporting said package;a spacer that extends from said base for abutment against said surfaceto provide a predetermined spacing between said leadframe and saidsurface; said leads are configurable such that, in a free state, saidleads extend toward said surface at least as far as said spacer, and inresponse to a combined weight of said package and said support member,said leads are capable of resiliently deforming such that said spacerabuts against said surface and said leads conformably engage with saidsurface; and a lead retainer extending outwardly and angularly from anend of said base and towards said surface; said leadframe includes afilm, and outer portions of said leads extend beyond said film; and saidouter portions are adapted to form a loop about said lead retainer; andsaid lead retainer has an outboard surface projecting laterally outwardrelative to said base.
 39. The support member of claim 38 wherein saidouter portions wrap around said outboard surface, around a free end ofsaid lead retainer and to an inboard surface of said lead retainer. 40.The support member of claim 38 wherein said lead retainer, said base andsaid spacer are formed as a single unitary unit.
 41. The support memberof claim 38 wherein said outer portions are attachable to an insidesurface of said lead retainer.
 42. The support member of claim 38wherein a lead bar is attached to said outer portions for attachment tosaid lead retainer.